Metals recovery



Oct. 2, 1956 F. L. PADGlTT METALS RECOVERY Filed NOV. 6, 1953 SODIUM CHLORIDE IN SMELTED LEAD-WEIGHT PERCENT 2 Sheets-Sheet 1 somum IN CHARGE WEIGHT PERCENT OF LEAD FIGURE INVENTOR.

FRANK L PADGITT BY I a I ATTORNEY Oct. 2, 1956 Filed Nov. 6, 1953 SODIUM CHLORIDE IN LEAD-WEIGHT PERCENT F. L. PADGlTT METALS RECOVERY 2 Sheets-Sheet 2 SMELTING TIME HOURS FIGURE 2 INVENTOR.

FRANK L PADGITT BY 7WJM ATTORNEY United States Patent METALS RECOVERY Frank L. Padgitt, Baton Rouge, La., assignor to Ethyl Corporation, New York, N. Y., a corporation of Delaware Application November 6, 1953, Serial No. 390,544

4 Claims. (Cl. 260437) This invention relates to improvement in the recovery of lead metal from process residues. More particularly, the invention relates to the recovery of lead metal from product residues characterized by being an intimate mixture of finely divided particles of lead and sodium chloride or other alkali chloride. Such residues are obtained from the production of tetraalkyllead compounds.

In the manufacture of tetraalkyllead compounds, such as tetraethyllead, for example, a comminuted sodium lead alloy is reacted with ethyl chloride under elevated temperature and pressure. The lead content is, in part, ethylated by the ethyl chloride. Thus, in employing monosodium lead alloy, NaPb, the theoretical reaction is From the foregoing, it is seen that a miximum of 25 percent of the available lead is utilized in the reaction, with at least 75 percent of the lead being discharged as unreacted metal. In practice, ideal reaction is not achieved, and as a result, only some percent of the lead charged is converted to tetraethyllead, leaving roughly 80 percent to be processed for recovery.

It is apparent that recovery of a large portion of the excess or unused lead is an important factor in the economics of the manufacture of such compounds. Even when other alloys of sodium and lead are employed in the ethylation operation, a large proportion of the lead fed is not converted to the desired tetraalkyllead compound and must be reprocessed. Thus, when employing an alloy having about 20 weight percent sodium content, about 70 percent of the lead must still be reprocessed.

In all cases, the unreacted lead in a product mixture is accompanied by substantial quantities of sodium chloride. Heretofore, prior to smelting and re-collecting the lead component of a reaction residue, the soluble chlorides have been removed by leaching the solids with water or aqueous solutions. Such a procedure allowed the smelting of the lead metal by more or less conventional techniques. Such aqueous pretreating gave rise to certain disadvantages, however. The leaching of the sodium chloride prevented any recovery of the sodium chloride on an economic basis. In addition, the aqueous treatment results in degradation, to the corresponding hydroxide, of any free alkali metal which might be present in the product mixture, and thus precluded recovery of such components. A further deficiency resultant from an aqueous step is the necessity of a relatively expensive drying operation prior to the smelting of the lead.

Attempts have previously been made to circumvent these disadvantages of a recovery system including one or more aqueous steps. Thus, the product mixture from an ethylation reaction has been treated with an anhydrous solvent for the tetraalkyllead. This successfully separates the tetraalkyllead and leaves the solids from which excess solvent is readily vaporized. Upon smelting, however, it has been found that production of a pure or at least homogeneous lead phase is not achieved. The lead was not separated from the accompanying sodium chloride in adequate degree for reuse. This deficiency is attributed at least in part to the fine state of subdivision of the sodium chloride particles, which apparently prevents a sharp Patented Oct. 2, 1956 separation of these components, even though the smelting was carried out at a temperature appreciably above the melting point of the sodium chloride.

This deficiency is observed in the solids residue fromv ethylated product mixtures from various types of ethylation techniques. Thus, the solids from a conventional reaction, where only a relatively small excess of ethyl chloride is employed, exhibit this limitation. Newer reaction techniques recently developed, which have certain inherent advantages, unfortunately produce residues which exhibit this deficiency in even higher degrees. Thus solids resultant from the Rodekohr et al. process, U. S. 2,574; 759, and the Neher et al. process, U. S. 2,644,827, unfortunately are more refractory with respects to satisfactory smelting than the solids from conventional ethylations. It appears that these ethylation techniques result in even more intimate mixtures of the lead and sodium chloride components.

The object of the invention, generally, is to provide a new and improved process for the separation and recovery of metallic lead from the solids residues from a lead alkylation reaction, such residues including finely divided particles of lead and a chloride of an alkali metal such as sodium chloride or potassium chloride. A more specific object is to provide a process which provides a higher degree of lead recovery from such mixtures at relatively moderate temperatures and at lower temperatures than otherwise feasible. Another object is to provide a process wherein not only the lead but also the alkali metal chloride is recovered for re-use. A further specific object is to provide an integrated process for the manufacture of tetraethyllead and recovery of the tetraethyllead and the metal values of the reaction product mixture, wherein the tetraethyllead formation reaction and the recovery operations are carried out under such conditions as to provide more efiicient recovery of these materials.

It has been discovered that the presence of unreacted sodium metal during the smelting operation provides for attaining the foregoing objects. According to the present invention generally, the process comprises carrying out the smelting operation in the presence of suificient metallic sodium to assure that the lead is collected as a homogeneous liquid phase virtually free of the metal chlorides originally present. The process is carried out at a sufliciently high temperature to liquefy the metal chloride, which is predominantly sodium chloride, and is collected as a liquid layer surmounting the molten lead layer. The so-collected chloride layer is virtually free of any occluded lead metal. Generally, the sodium required for effective operation must be present in proportions of at least 1 percent by weight of the lead metal, and normally a somewhat higher proportion is preferred. As described hereafter, the sodium metal may be incorporated in the heterogeneous solids residue in any of several manners. In one form of the process, the formation of the'tetraalkyllead is carried out under such conditions as to provide a product mixture wherein the solids components include metallic sodium in the proportions of about at least one percent of the lead metal present.

The process is generally applicable to the lead metal containing residues of the character described. Most specific benefits are found in processing the residues from a tetraalkyllead forming reaction. The alkylleads are produced by the alkylation of an alkali metal lead alloy with an akyl chloride, giving rise to the mixtures from which the metals are to be recovered by the present process. Normally, an alloy consisting essentially of sodium and lead is used, but the process is applicable to solids from the ethylation of a ternary alloy, which would contain minor amounts of a third metal component such as potassium or magnesium. The examples and data hereafter given show the application of the process in conjunction with the residues from a tetraethyllead process, but it is also readily adaptable to lead containing residues from formation of other alkyllead compounds such as tetraisopropyllead, dimethyldiethyllead, tetramethyllead, and the like. In addition to the examples hereafter given, the details of preferred conditions for the process are demonstrated by the accompanying figures wherein Figure 1 is a plot showing the effect, on purity of lead recovered, by the co-present sodium metal in varying amounts. Figure 2 is a plot showing graphically the effect of co-present sodium in reducing the smelting time required to achieve satisfactory lead purity.

As already indicated, the sodium metal concentration required for the process can be incorporated into the reaction solids residues in several different manners. All of these modes of addition provide similar results, with respect to the etficiency of the smelting operations to recover the lead metal values. However, the ease of providing the required sodium varies for these different embodiments of the process. One suitable way of incorporating the sodium metal is to add sodium in massive form below the surface of the charge in. a smelting operation. Another somewhat more effective method providing the sodium is to blend a comminuted sodium lead alloy with the dry reaction solids from which the tetraalky-llead has been substantially removed. Another and particularly effective method of providing the sodium in a very uniform distribution through the heterogeneous solids mixture is to adjust the alkyl-ation reaction conditions so that the sodium is not completely, or virtually completely, consumed during the alkylation, but instead is only partially consumed and a desired concentration is retained as the metal in the reaction products. The working example following illustrates this preferred mode of operation.

Example I Tetraethyllead was prepared in the following manners. A charge of finely divided monosodium lead alloy was introduced in an ethylation autoclave along with pure ethyl chloride in the proportions of about 200 parts by weight of ethyl chloride to .100 parts of .alloy. The alloy was protected from degradation by reaction with at mospheric components by blanketing with a dry inert gas durin the char ing operations. After charging, the autoclave was immediately sealed and the contents reacted'at a temperatur'e of about 80 C. for a period of less than one hour. The autoclave and contents were then rapidly cooled to assure that no further reaction occurred.

The product of the foregoing ethylation was then treated with additional ethyl chloride and the tetraethyllead formed was thus extracted. The solid components were drained and dried leaving a heterogeneous, finely divided mixture having the following composition:

Weight percent Lead metal 76.9 Sodium chloride 18.7 Sodium 3.3' Tetraethyllead about .05

This solids mixture was then charged to a smelting chamher to an initial working depth of about five feet. The surface of the charge was blanketed with a moving stream of dried and deoxidized nitrogen gas. Heating of the charge was started and the temperature raised gradually to an operating temperature of approximately 900 C. The temperature was maintained at this operating level for about 3 hours. The charge was then cooled, and a static sample was taken. The sample was a cylinder sample through the entire depth, which .at this time consisted of a lower layer which was substantially all lead metal, plus most of the sodium metal originally charged, surmounted by a layer consisting essentially of fused sodium chloride. The static, sample referred to. was quickly frozen and'sub-samples' taken at different vertical levels to ascertain the composition of the several layers at various vertical positions. It was found that the lead layer was virtually free of salt, that is, the sodium chloride content was less than 0.01 weight percent even within two inches of the sodium chloride layer. In addition to the high degree of purity With respect to elimination of sodium chloride, the lead layer represented a high degree of recovery, of the order of 98 percent, of both the lead and sodium components of the original charge.

As contrasted to the foregoing example, Example 11, below, shows the results'obtained if the solids smelted do not contain the necessary amount of sodium metal.

Example II Tetraethyllead was prepared in a similar manner as described in Example I, except'that the ethylation conditions were maintained for an extensive period, sufficient to provide maximum yield. As a result, the solids obtained after separation of the tetraethyllead contained only a trace (less than 0.01 weight percent) of metallic sodium.

After smelting and sampling as in the preceding example, it was found that the lead layer was contaminated by substantial quantities of sodium chloride. The sodium chloride concentration was 6.6 weight percent .as far as live inches below the salt layer, and about 12 percent at a point one inch below the salt layer.

The foregoing examples demonstrate the importance of an appreciable quantity of metallic sodium present during the smelting operation. To further illustrate the effect of the sodium, a number of additional smelting operations were carried out. The solids processed were theresidues obtained by ethyl-at-ing different physical forms of alloy. In most cases, the sodium content of the solids processed was adjusted by altering the reaction conditions, but in some instances extraneous sodium was added to the solids mixture.

The results of this series of runs are presented graphically by Figure 1, which is a plot of the variation in concentration of sodium chloride contaminant in the smelted lead layer against the concentration of sodium met-a1 expressed as weight percent of the lead metal originally present. Referring to'Figure 1, it is seen that superior purity of the lead layer is obtained when the sodium content is virtually one percent or more, the sodium chloride content being so low as to be non-detectable in the concentration range of 'hundredths of a percent.

As already mentioned, reaction residues from a variety of ethylationprocesses were processed in obtaining the data shown by Figure 1. Thus, residues from ethylations carried out according to the Rodekohr et .al. process, U. S. 2,574,759, and by the Tanner process, U. S. 2,635,107, were treated and consistent results were obtained.

The sodium required for successful operation of the smelting process can thus be provided by terminating the ethylation of the most commonly used alloy, monosodium lead alloy, Na'Pb 10 Weight percent sodium) at a time before the sodium is fully reacted. A desirable variation in this mode of providing sodium involves increasing the initial sodium content. It has been found that small increases in the sodium content of the original alloy (above the'NaPb composition) can be provided without a substantial adverse effect on the ethylation efficiency. Accordingly, a preferredmode of providing involves the ethylation of an alloy containing up toabout ll weight percent sodium. This mode of operation allows'production of about the same quantity of tetraethyllead in each reaction cycle, and, concurrently provides the metallic sodium required for efficient smelting according to the present process. 7

As heretofore mentioned, alternative land highly effective method of introducing the sodium metalregained in the smelting operations is to blend the solids with the required amount of a comminuted sodium lead alloy. The use of an alloy of sodium and lead is beneficial in several regards. Uniform distribution of the sodium metal through the heterogeneous mixture is facilitated. in add Ion, an alloy of lead, although quite reactive, is not so ea ly graded by moisture in gaseous atmosphere as is SOditlDl metal per so. A further advantag-e lies in the lo e tendency of the sodium component to be lost by vapc ticn. The process, it will be noted, can, generally, be very successfully 01 ated at ten oera tures above the vaporization tempera are or" metallic sodium. This is surprising, but is believed to be attributable to the fact that even if added sodium is initially vaporized, the vapors tend to be absorbed by the liquid lead rather than to escape into the atmosphere above charge. l-lowever, if a massive for nr"or example, a cast brickof sodium is charged, there is a nite tendency for vaporization of the sodium to occur before there has been an opportunity for absorption in the lead. The addition of sodium in the to -r. of a comminuted sodium lead alloy circunr-rents this dificulty. it is preferred to utilize an alloy having a sodium concentration of it) percent. To provide the desired composon range of the mixture fed to the smelting operation, this is mixed with the reaction solids in the proportions of from about 8 to 30 parts by weight to 100 parts of the solids from the ethylation process. An example of this embodiment of the process is given below.

Example HI the solids. The mixture then had the following gross composition:

Weight percent Lead 76.5 Sodium 19.9 Lead oxide 1.1 Sodium metal 2.1

The so-formed blended mixture was then charged to a smelting vessel and smelted as in preceding examples. After smelting for several hours at 903 C., the analysis of the lead layer at a point only one inch below the salt layer did not show any detectable sodium chloride. A high degree of recovery of the lead and sodium metal was obtained, approaching 98 percent.

One of the particular benefits of the process is the rapidity with which the smelting operation is carried out. This advantage is graphically illustrated in Figure 2. Referring to Figure 2, a plot, A, is shown of the sodium chloride retained in the lead layer during an extended smelting period, the initial charge having only 9.2 weight percent lead sodium metal, Although a lead layer was rapidly formed during this operation, the sodium chloride contaminant was only slowly reduced, in that, for example, -the salt content was still 3.8 weight percent after smelting for a 3 hour period at 909 C. Continuation of smelting of this charge showed that at least a 39 hour smelting period was required, before the concentration or" sodium chloride impurity dropped to a satisfactorily low level.

In contrast to the extremely slow rate of satisfactory smelting shown by plot A, when a charge containing 1.9 weight percent sodium is processed, the rate of obtaining a purified lead layer is quite high indeed. Plot B represents the decrease in sodium chloride content in the lead layer when metallic sodium in the charge has been so provided. It will be seen that in the relatively short period of three hours, the lead layer is entirely freed of the sodium chloride contaminant.

As heretofc "e described, the preferred proporhons of sodi u in the charge to the smelting operations 0 ercent sodium or above. Although no precise limit to the sodium content has been observed, it

is pre erred to operate with less than about 3 percent r. The process of recovery of a predominantly lead metal free or" s 1 chloride impurity from a heterogeneous solids r .ture derived from a lead alkyla-tion process, said solids mixture being characterized by consisting essentially of an intimate mixture of finely divided lead and finely div ed sodium chloride particles, comprising smelting said mixture at a temperature above the melting point or" sodium chi ride in the presence of metallic sodium in at least the proportions of one percent of the lead metal in the mixture.

2. The process of manufacture of tetraethyllead by the ethylation of sodium lead alloy and the recovery of tetraethyllead, and unreac-ted sodium chloride free lead and sodium from the ethylated mixture comprising ethyla-ting a sodium lead alloy with ethyl chloride, terminating the ethylation while unreacted sodium is present in the proportio s of at least one percent of the unreacted lead, 5 the tetraethyllead and excess ethyl chloride under anhydrous conditions, and smelting the so-formed solids residue at a temperature above the melting point of sodium chloride for a period suflicient to form a sodium chloride free lead layer and a substantially lead free sodium chloride layer.

3. The process of manufacture of tetraethyllead by .216 ethylation of sodium lead alloy and the recovery of tetraethyllead and unreacted, sodium chloride free unreacted lead and excess sodium from the ethylated mix ture comprising ethylating a sodium lead alloy having from 10 to weight percent sodium with ethyl chloride in the proportions of at least two parts by weight of ethyl chloride to one part alloy, terminating the ethylation while unreacted sodium is present in the proportions of at least one percent by weight of the unreacted lead, separating the tetraethyllead and excess ethyl chloride under anhydrous conditions, and smelting the so-formed solids residue at a temperature of from about 850 t 960 C. for a period of from one to three hours, forming thereby a predominantly lead layer free of sodirlm chloride and a sodium chloride layer substantially free of lead.

4. The process of recovery of a predominant y lead metal free or" sodi in chloride impurity fro .1 a heterogeneous solids mixture derived from the ethyl chloride ethylation of monosodium lead alley, said solids mixture being characterized by consisting essentially of an intimate mixture of finely divided lead and finely divided sodium chloride particles, compri 'ng blending said solids mixture with corm linuted monosodium lead alloy in the proportions of from about 8 to 30 parts by weight of alloy to lG-(l parts by weight of the said solids mixture, then smelting at a temperature oi above 801 to about 900 C. for a per od of from one to three hours, forming thereby a predominantly lead layer free of sodium chloe and a sodium chloride layer substantially free of epara References tilted in the file of this patent UNITED STATES PATENTS 2,'c 6l,36l randiean Dec. l, 1953 

2. THE PROCESS OF MANUFACTURE OF TETRAETHYLLEAD BY THE THYLATION OF SODIUM LEAD ALLOY AND THE RECOVERY OF TETRAETHYLLEAD, AND UNREACTED SODIUM CHLORIDE FREE LEAD AND SODIUM FROM THE ETHYLATED MIXTURE COMPRISING ETHYLATING A SODIUM LEAD ALLOY WITH ETHYL CHLORIDE, TERMINATING THE ETHYLATION WHILE UNREACTED SODIUM IS PRESENT IN THE PROPORTIONS OF AT LEAST ONE PERCENT OF THE UNREACTED LEAD, SEPARATING THE TETRAETHYLLEAD AND EXCESS ETHYL CHLORIDE UNDER ANHYDROUS CONDITIONS, AND SMELTING THE SO-FORMED SOLIDS RESIDUE AT A TEMPERATURE ABOVE THE MELTING POINT OF SODIUM CHLORIDE FOR A PERIOD SUFFICIENT TO FORM A SODIUM CHLORIDE FREE LEAD LAYER AND A SUBSTANTIALLY LEAD FREE SODIUM CHLORIDE LAYER. 